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Explanation
Solving a quadratic inequality by graphing is not difficult if you remember the basics of graphing a quadratic equation. When graphing quadratic inequalities, first graph the quadratic equation then pick a point that is not on the parabola itself and plug it into the original inequality. If the statement is true, shade in the area where that point lies. If the statement is false, shade in the other area.
Transcript
Solving a quadratic inequality graphically.
What we do with a quadratic inequality is very similar to what we do with a linear inequality.
Basically what we want to do is sketch the curve and then choose a test point to see which side we're going to shade. We'll do a very simple example behind me.
What I have is Y is less than X squared. Basically what we want to do is view this as an equality, and then sketch the graph.
So we know that Y equals X squared is just a parabola, vertex at the origin. Just like with linears, this one is strictly less than. That tells us we have a data line because things on this line aren't going to satisfy this inequality. So we basically sketch our parabola with a dotted line, and then choose a test point. Okay.
Your point can be anything you want. Just make sure it is not on the parabola. So choose something safe. We'll look at the point, say, 0, 1 and all we have to do is plug that in and see if we get a true or false statement.
We plug in 0, 1, what we end up with is 0 is greater than 1. That's a false statement. So that tells me that this point inside doesn't actually satisfy this inequality. So I shade the other portion.
If I got a true statement I would shade that side, false statement shade the other. So what we end up with is everything outside of this parabola.
Now solving a quadratic inequality, just plot your graph, choose your test point and shade the appropriate region.
